This invention relates generally to direction and flow control valves capable of proportionally controlling a number of loads under positive and negative load conditions.
In more particular aspects this invention relates to fluid control valves provided with positive and negative load compensation.
In still more particular aspects this invention relates to negative load compensation, of a direction and flow control valve, in which fluid flow from each of the actuator ports is individually compensated.
Closed center fluid control valves, pressure compensated for control of positive and negative loads, are desirable for a number of reasons. They permit load control with reduced power losses and therefore increased system efficiency. They also permit simultaneous proportional control of multiple positive and negative loads. Such fluid control valves are shown in my U.S. Pat. No. 4,180,098, issued Dec. 5, 1979 and also in my U.S. Pat. No. 4,222,409, issued Sept. 16, 1980. The negative load compensation of the valves of those patents suffers from certain unobvious disadvantages.
In the valve of U.S. Pat. No. 4,180,098 the flow of fluid, under negative load pressure, is delivered from one load chamber, through passage leading past two transfer tubes in the comparatively long transverse core, to the negative load compensator and therefore is subjected to a substantial pressure drop, before it enters the compensator, while the fluid flow from the other load chamber directly enters the compensator. This factor influences the magnitude of the control pressure differential in a different way for each of the load chambers and is therefore undesirable. The existance of large resistance to flow in the exhaust branch of the circuit also decreases efficiency, when controlling a positive load while the valve size becomes larger and the transfer tubes themselves create an additional cost.
In the valve of U.S. Pat. No. 4,222,409 the flow of fluid, under negative load pressure is delivered from one load chamber, through a passage provided in the hollow spool, to the negative load compensator providing large resistance to flow, large unbalance in control pressure differentials, severe limitation in maximum fluid flow through the valve, large throttling and therefore efficiency loss, increase in valve length and increase in cost.